Conventionally, an austenitic stainless steel, typified by SUS304, has been used for parts for which corrosion resistance and a non-magnetic property are required. However, if SUS304 is subjected to working, deformation induced martensite transformation occurs, and magnetic property is generated. For this reason, SUS304 cannot be applied to parts requiring the non-magnetic property.
Conventionally, a high Mn and high N stainless steel, which exhibits a non-magnetic property after working is applied, has been used for parts for which the non-magnetic property is required in a state of being subjected to working and not subjected to any treatment after the working (for example, see Patent Documents 1, 2, and 3).
However, the high Mn and high N stainless steel has high strength, which means that it is difficult to form the high Mn and high N stainless steel into a complicated shape by cold working. Furthermore, if the high Mn and high N stainless steel is formed into a complicated shape by cold working, a very slight amount of deformation induced martensite transformation occurs, and the steel exhibits a low magnetic property. Thus, the super non-magnetic property cannot be obtained.
To deal with this, conventionally, the steel described above is subjected to cutting work so as to have a predetermined shape in order to avoid the occurrence of deformation induced martensite. However, this poses a problem of high cost.
In addition, Cu, Al and the like have been used as additional elements in the case where the steel is used in a state of being subjected to cold working to form the steel into a complicated shape and not subjected to any treatment after the cold working. However, Cu or Al leads to problems, for example, of reduced corrosion resistance, reduced strength.
It should be noted that the super non-magnetic property as used in the present invention represents, for example, a level of a magnetic flux density of 0.01 T or less (preferably, 0.007 T or less) that a product indicates when placed in a magnetic field at 10000 (Oe).
A conventional high Mn and high N stainless steel having non-magnetic property has a magnetic flux density of 0.05 T or less after being subjected to cold working, which satisfies a practical level of a non-magnetic property. However, this does not satisfy a level of a super non-magnetic property that the present invention requires.
Meanwhile, there is proposed a material which is a high Mn stainless steel including Cu and achieving improved cold workability (see, for example, Patent Document 4). However, if this material is subjected to cold working to form the material into a complicated shape as described above, a slight amount of low magnetic property is generated, which poses a problem in that the super non-magnetic property required in the present invention cannot be obtained.
Furthermore, it can be considered to subject a near-net shaped stainless steel wire having a modified shape which is close to the final part shape to molding into a complicatedly shaped product such as a steel wire for a cable connector, and the like. For example, Patent Document 5 describes a technique of subjecting a base wire having a modified cross section to twist working. However, at the time of manufacturing a steel wire coil having a modified cross section with a near net shape, a steel wire having been subjected to shape-modifying work is annealed and coiled, and this causes an inconvenience in that the cross-sectional shape of the steel wire is more likely to be crushed or defects are more likely to occur in the steel wire. This poses a problem in that, substantially, it is not possible to manufacture a soft steel wire coil having a modified cross section with a near net shape, other than that having a simple, plate-like shape.
The conventional high Mn stainless steel wire rod or steel wire is not a material that has, in addition to corrosion resistance, both sufficient cold workability and super non-magnetic property in a state of being subjected to cold working and not subjected to any treatment after the cold working. Furthermore, with a conventional technique, the cross-sectional shape of the steel wire is crushed or defects occur at the time of manufacturing; and therefore, a soft steel wire coil having a modified cross section with a complicated near net shape cannot be substantially manufactured.